1. Field of the Invention
The present invention relates to ophthalmic lenses, and more particularly to the design of translating contact lenses which are truncated for correcting presbyopia and whose design is optimized to maximize translation ability while maintaining comfort when the lens is worn on eye.
2. Discussion of the Related Art
Contact lenses are considered medical devices and may be worn to correct vision and/or for cosmetic or other therapeutic reasons. Contact lenses have been utilized commercially to improve vision since the 1950s. Early contact lenses were made or fabricated from hard materials, and were relatively expensive and fragile. Although these contact lenses are still utilized, they are not suitable for all patients due to their poor initial comfort. Later developments in the field gave rise to soft contact lenses, based upon hydrogels, which are extremely popular and widely utilized today. The introduction of soft contact lenses has significantly improved the comfort experienced by the wearer.
As a person ages, the crystalline lens gradually becomes more rigid, and thus their eyes are less able to accommodate. Said another way, our eye muscles ability to alter the shape of the natural human crystalline lens to focus on near objects is diminished as we age. This condition is known as presbyopia. In treating presbyopic patients, one innovation is the use of translating lens designs. Two of the more popular types of translating lens designs can be of the truncated variety or the pseudo-truncated variety with the primary difference between the two being the overall lens shape and how the inferior portion of the lens interacts with the eyelids to achieve translation of the lens relative to the pupil. The typical translating lens relies on the relative movement of the contact lens relative to the eye, specifically the pupil. Typically the translating lens will have multiple optical zones, but unlike a typical concentric bifocal, where the vision correction zones are annular regions concentrically located, in the translating bifocal, the vision correction zones are located in upper and lower positions. At a minimum, both a near and far vision correction zone would be present in the lens to account for the loss of the patients ability to accommodate, and depending on the angle of gaze, one can optimize vision by directing the gaze through one zone or the other. To accomplish this, the near and far zones are generally placed inferior and superior respectively. As an example, as one looks downward (typically for near vision needs such as reading) they are looking through the lower (near) portion of the lens. This is successful because the lens, through interaction with the lower eyelid, is typically driven upward, relative to the pupil, whose angle of gaze is being directed downward. As their gaze returns to a more horizontal position and the lens wearer looks to objects in the distance, the relative position of the lens is such that the pupil of the eye is now aligned with looking through the superior (far) portion of the lens. This results in optimizing the focus for both near and far vision needs. The incorporation of one or more intermediate zones between the near and far zones may also be present to facilitate intermediate vision needs such as computer viewing.
Thus to achieve optimal vision for the multiple vision needs, it is essential to achieve the necessary movement of the translating lens relative to the eye for a translating lens to function correctly. Not achieving this may result in the gaze being directed through the wrong zone or a portion of both zones and thus resulting in blurred vision. One of the early concepts in this space is discussed in U.S. Pat. No. 6,109,749, in which the innovators incorporated an integrally formed bevel that provided for a type of buttress or protrusion from the anterior lens surface to interact with the eye-lid in order to aid in translating the lens relative to the eye itself. With the issue of comfort put aside for the time being, while the approach of lens interaction with the lower eyelid is indeed viable, the extent of the relative translation of the lens may be impacted by a number of items including but not limited to the quality and presence of the tear film, lens fit, lens design, and the asymmetry of the eye and how it interacts with the contact lens thus impacting, or in some cases not allowing, the desired result to be achieved.
In U.S. Pat. No. 6,746,118, which also attempts to achieve vertical lens movement, the innovator suggests that the dual nature of the secondary prism is an improvement over the '749 patent accomplished by achieving a secondary power in addition to facilitating the vertical shifting of the lens. But this issue is a bit more complicated than that as there are other factors that neither the '749 or the '118 patent consider, for example, U.S. Pat. No. 7,216,978 illustrates that the upper and lower eyelids do not move strictly in a vertical direction during blinking. Rather, the upper lid moves substantially vertically, with a small nasal component during blinking, and the lower lid moves substantially horizontally, moving nasal-ward during blinking. Given the primarily horizontal movement of the lower lid, one may question its extent of contribution to vertical lens translation; at best it can only serve as a stop to prevent the lens from moving downward. Additionally, the upper and lower eyelids are not symmetrical with respect to a plane cutting though the vertical meridian. In other words, individuals do not blink symmetrically relative to a horizontal axis drawn between the open upper and lower lid. This, at a minimum, may have an impact to the required vertical translation of the lens that these innovators are all trying to achieve. Accordingly, blinking in of itself may not be the only leveragable item in the ideal translation of the contact lens thus presenting yet another opportunity to improve upon the design in order to maximize the extent of lens translation.
Another aspect related to blinking, which may come into play when one is dealing with maintaining comfort, is the presence of mechanical receptors in both the upper and lower eyelids. While it is not fully known whether there are differences in the sensitivity of the receptors in the upper or lower eyelids, what is known is that the distance travelled by the upper eye-lid is greater than that of the lower eyelid during a blink. Given that these mechanical receptors respond to changes in stress, smoother and less abrupt changes in geometry will likely perform better than those designs with abrupt changes in geometry. Since the distance travelled by the upper eyelid is greater, it is probable that its mechanical receptors are more likely to encounter increased opportunities to respond to changes. All things being equal, given the greater duration of the lens-lid interaction with the upper eyelid, it follows that one may want to consider the upper eyelid's interaction with the lens equally, if not more so, than that of the lower eyelids interaction. Additionally, the nature of a soft contact lens as compared to a hard contact lens, may also impede the ability of the soft contact lens to translate effectively given it is more likely to conform to the shape of the cornea. Consideration of the shape of the posterior surface of the lens and how this may impact lens translation can be extremely important and is something the previous innovators in this space have not addressed in combination with translating lens concepts.
In the truncated translating lens design the lower portion of the truncated contact lens is flattened by cutting off or shortening that part of the lens resulting in a non-circular lens. The conventional truncated translating lens design results in a substantially flat, thick edge at the bottom of the lens. The intent being that this flattened portion interacts with the lower eye-lid to achieve translation by the lid serving as a positive mechanical stop when it interacts with the bottom of the lens. Exemplary descriptions of such lenses are set forth in a number of patents, including U.S. Pat. No. 7,543,935, U.S. Pat. No. 7,430,930, U.S. Pat. No. 7,052,132, and U.S. Pat. No. 4,549,794. However, a relatively flat edge on contact lenses such as these may tend to influence comfort. An alternative approach which leverages the concept of a minimum energy position is that which is provided in U.S. Pat. No. 7,810,925, in which a lens design with two discrete stability positions is suggested to optimize lens position for near and distance vision needs. This concept of minimum potential energy position may be leveraged to achieve these two stability positions. However, given that some level of displacing force (potentially a significant level in the '925 patent case) is required to move from one position to the other, it's likely that some level of discomfort is also being introduced for the initial stability position to be overcome in order to move to the second stability position. Comfort can be as, if not more, important that achieving the desired displacement of the lens.
Innovators have also attempted to use a pseudo-truncated design for a translating lens design. In the pseudo-truncated translating lens approach, the lens remains circular, but through localized thickness changes a pseudo truncation zone is created that interacts with the eyelid to achieve the desired translation of the lens through interaction with the eyelids. One such example is shown in U.S. Pat. No. 6,921,168. In the '168 patent a ramped ridge zone located in the inferior portion of the lens and is positioned below the optical zone. The ramped ridge zone of the lens is intended to remain underneath the lower lid. The lens also includes what they call a ridge-off zone which is located medially, laterally and superiorly in the peripheral region of the lens, essentially everywhere else the ramp ridge zone is not. It is the intent of the innovators that the lower eyelid of the eye is engaged with at least some portion of the ramped ridge at all times. It is this interaction between the lower eyelid and the lens that the innovators of the '168 patent claim how the desired translation of the lens is achieved. The '168 patent attempts to improve comfort by attempting to design the ramped rigid zone to better conform to the lower eyelid. While these innovators speak to the need to conform to the lower eyelid and gradually engage the lower eyelid which is achieved by the presence of the ramped ridge zone, no consideration is given to placement and extent of the ramped rigid zone itself which is fairly localized in the inferior region alone. While the innovators of the '168 patent discuss the posterior surface of the lens containing an optical zone, no attention or discussion is given to the posterior surface or shape of the lens as it relates to lens translation. Additionally, no mention of the impact of how the upper eyelid interacts with the ridge-off zone region and its impact to translation and comfort is provided.
In US Published Patent Application Numbers 2012/0075579 and 2012/0075581, whose assignee is also the assignee of applicants' present invention, a translating lens for correcting presbyopia having a pseudo-truncation is provided. In this case, the pseudo truncation is asymmetric with respect to the vertical meridian, specifically the pseudo-truncation is biased in the inferior and nasal directions which more closely corresponds and is aligned to how our gaze is directed during near work. When we focus on near items, our gaze is directed both downward and inward, as each eye tends to converge nasally to better view the near item. This is in contrast to distance gaze where each eye is directed more horizontally and parallel to each other in order to better view the distant object. While the asymmetric aspects of this innovation do consider both the horizontal and vertical movement of the lower eyelid and worthy to consider in a translating lens design particularly as it relates to its impact to translation of the lens, additional opportunity still exists in this space.
In US Published Patent Application Number 2013/0258274, whose assignee is also the assignee of applicants' present invention, a lower eyelid contact surface and under-lid support structure is disclosed that suggests varying ramp shape configurations including both convex and concave curved portions. Applicants believe this is an important consideration as well, but US Published Patent Application Number 2013/0258274 does not consider these ramp shapes in combination with parametrization of the back radius of curvature, nor do they consider them in combination with several of the design elements of applicant's invention simultaneously and or holistically.
Lastly, in U.S. Pat. No. 6,241,355, the innovators use spline based mathematical surfaces without restrictions of rotational symmetry in order to enable the design and fabrication of contact lenses that have posterior surfaces that provide a good fit to corneas of complicated shapes. Although the general approach of fitting splines to ensure a smooth and continuous surface may be utilized in the present application, the innovators do not describe or consider the unique geometry and features of the present application in the '355 patent. Rather their primary purpose was to enable an improved fit to irregularly shaped corneas, such as those found in keratoconus patients.
The prior art devices described above, while representing a considerable improvement over older devices, employ features and designs resulting in certain tradeoffs, for example, and most relevant to applicant's invention, comfort versus the extent of translation and how this translation is achieved. Of the art discussed, while each attempts to address the issue from a specific aspect, they do so from unique perspectives rather than from a more holistic approach as is accomplished with the present application. Furthermore, even when one combines these prior art references, they do not provide the physical structure or relationship of the present application. Accordingly, there exists a need for a truncated translating contact lenses with improved on eye performance that takes into account the anatomy of the eye and the functioning of the eye-lids from multiple design considerations such as value and shape of thickness variations in combination with posterior radii variations while also maintaining a high degree of comfort when such a lens interacts with both the upper and lower eyelids. Having a lens that accomplishes this in combination with optimizing both far and near vision needs would be advantageous.